Photoelectrochemical properties of Ni-doped Fe2O3 thin films prepared by electrodeposition

Ni-doped Fe 2 O 3 thin films which were active photoanodes for water splitting were prepared by electrodeposition. By adjusting Ni molar ratios (Ni/(Ni   +   Fe)) in the electrolyte, Fe 2 O 3 thin films with various compositions of Ni could be tuned. The films were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic absorption spectrophotometer, and UV–vis spectroscopy. The highest photo-response obtained from Fe 2 O 3 doped with 2.08   mol.% Ni is 1.5   mA/cm 2 at 0.65   V vs. Ag/AgCl in 1.0   M NaOH solution. The high performance is attributed to the improvement of charge transport properties and retardation of the charge recombination resulting from the dopants in the lattice. The optical absorption spectra of the films reveal that the bandgaps of the Ni-doped Fe 2 O 3 films are approximately 1.9–2.2   eV for all samples regardless of their doping level. XPS shows that the concentration of Ni is much higher on the surface than that in bulk.